Java Oops Quiz

Reviewed by Godwin Iheuwa
Godwin Iheuwa, MS (Computer Science) |
Database Administrator
Review Board Member
Godwin Iheuwa, a Database Administrator at MTN Nigeria, holds an MS in Computer Science, specializing in Agile Methodologies and Database Administration from the University of Bedfordshire and a Bachelor's in Computer Science from the University of Port Harcourt. His proficiency in SQL Server Integration Services (SSIS) and SQL Server Management Studio contributes to his expertise in database management.
 , MS (Computer Science)
By Srividya A
Srividya A, Software Engineer
Srividya A G is a software engineer who enjoying taking and creating quizzes on various topics.
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  • 1/10 Questions

    What is the primary purpose of inheritance in Java?

    • Code reusability
    • Data hiding
    • Access control
    • Memory management
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About This Quiz

Object-oriented programming (OOP) is a fundamental paradigm in Java, enabling the creation of modular, reusable, and maintainable code. This Java OOP quiz delves into the core principles of Java OOP, challenging your understanding of abstraction, encapsulation, inheritance, and polymorphism.

In this quiz, you will encounter questions that assess your knowledge of classes, objects, constructors, access modifiers, interfaces, abstract classes, and method overriding and overloading. This is your opportunity to demonstrate your grasp of these essential concepts and showcase your ability to apply them effectively in Java programming. This quiz offers an invaluable opportunity to expand your knowledge and improve your programming abilities.

Java Oops Quiz - Quiz

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  • 2. 

    Which access modifier restricts access to a class member to within the same class only?

    • Public

    • Protected

    • Private

    • Default

    Correct Answer
    A. Private
    Explanation
    The private access modifier is the most restrictive access level in Java. It limits access to a class member (field or method) to within the same class only. This enforces encapsulation by preventing external code from directly accessing or modifying the internal data of an object.

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  • 3. 

    What is the keyword used to declare an interface in Java?

    • Interface

    • Class

    • Abstract

    • Extends

    Correct Answer
    A. Interface
    Explanation
    An interface in Java is a contract that defines a set of methods that implementing classes must provide. It specifies the behaviors that classes should exhibit but doesn't provide the implementation details. Interfaces promote abstraction and flexibility in code design.

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  • 4. 

    What is the purpose of encapsulation in Java?

    • Improve code readability

    • Increase code complexity

    • Protect data integrity

    • Optimize program performance

    Correct Answer
    A. Protect data integrity
    Explanation
    Encapsulation is the practice of bundling data (fields) and the methods that operate on that data within a class. It restricts direct access to the data from outside the class, forcing interaction through defined methods. This protects data integrity and promotes modularity.

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  • 5. 

    What is the difference between method overriding and method overloading?

    • Overriding changes method signature, overloading doesn't

    • Overloading changes method signature, overriding doesn't

    • Overriding provides a new implementation, overloading provides multiple methods with the same name

    • They are the same

    Correct Answer
    A. Overriding provides a new implementation, overloading provides multiple methods with the same name
    Explanation
    Method overriding involves providing a specific implementation for a method that is already defined in a superclass. This allows subclasses to customize inherited behaviors. Method overloading, on the other hand, involves defining multiple methods with the same name but different parameters in the same class.

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  • 6. 

    What is the role of a constructor in a Java class?

    • Define class methods

    • Declare class variables

    • Initialize object state

    • Control access to members

    Correct Answer
    A. Initialize object state
    Explanation
    A constructor is a special method with the same name as the class. It is automatically called when a new object of that class is created. Its primary role is to initialize the object's fields, ensuring that the object starts in a valid and usable state.

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  • 7. 

    What is the purpose of the this keyword in Java?

    • Refer to the current class

    • Refer to the parent class

    • Refer to the current object

    • Refer to a static method

    Correct Answer
    A. Refer to the current object
    Explanation
    The this keyword in Java refers to the current object within a non-static method or constructor. It's used to differentiate between instance variables and local variables or method parameters when they have the same name. It can also be used to call other constructors within the same class.

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  • 8. 

    Can an abstract class have non-abstract methods?

    • Yes

    • No

    • Only if it has abstract methods

    • Only if it inherits from another abstract class

    Correct Answer
    A. Yes
    Explanation
    An abstract class can have both abstract and non-abstract methods. Abstract methods are declared without an implementation, acting as placeholders for subclasses to provide concrete implementations. Non-abstract methods have complete implementations and can be used directly by the abstract class or its subclasses.

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  • 9. 

    Which principle allows objects of different classes to be treated as objects of a common type?

    • Abstraction

    • Encapsulation

    • Polymorphism

    • Inheritance

    Correct Answer
    A. Polymorphism
    Explanation
    Polymorphism, meaning "many forms," allows objects of different classes to be treated as objects of a common type. This is achieved through method overriding, where a subclass provides a specific implementation for a method already defined in its superclass. At runtime, the appropriate method is called based on the actual object's class.

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  • 10. 

    What is the difference between an abstract class and an interface?

    • An abstract class can have constructors, an interface cannot

    • An interface can have constructors, an abstract class cannot

    • An abstract class can be instantiated, an interface cannot

    • An interface can be instantiated, an abstract class cannot

    Correct Answer
    A. An abstract class can have constructors, an interface cannot
    Explanation
    An abstract class can have constructors, while an interface cannot. Constructors are used to initialize the state of an object when it's created. Since interfaces cannot be instantiated directly, they don't have constructors. Abstract classes, however, can be used as base classes for inheritance.

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Godwin Iheuwa |MS (Computer Science) |
Database Administrator
Godwin Iheuwa, a Database Administrator at MTN Nigeria, holds an MS in Computer Science, specializing in Agile Methodologies and Database Administration from the University of Bedfordshire and a Bachelor's in Computer Science from the University of Port Harcourt. His proficiency in SQL Server Integration Services (SSIS) and SQL Server Management Studio contributes to his expertise in database management.

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  • Current Version
  • Oct 04, 2024
    Quiz Edited by
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    Expert Reviewed by
    Godwin Iheuwa
  • Dec 02, 2011
    Quiz Created by
    Srividya A
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